8
views
0
recommends
+1 Recommend
1 collections
    0
    shares
      • Record: found
      • Abstract: found
      • Article: not found

      Oxygen therapy limiting peripheral oxygen saturation to 89-93% is associated with a better survival prognosis for critically ill COVID-19 patients at high altitudes

      research-article
      a , b , c , d , b , c , b , e , f , e , h , g , g , h , g , h , *
      Respiratory Physiology & Neurobiology
      Published by Elsevier B.V.
      COVID-19, liberal oxygen therapy, intensive care unit, high-altitude, central respiration, normoxemia, hypoxemia, hyperoxemia, ICU, intensive care unit, FiO2, inspired oxygen fraction, PaO2, arterial partial pressure of oxygen, PB, barometric pressure, ARDS, acute respiratory distress syndrome, NIV, non-invasive ventilation, HFNC/NRM, high-flow nasal cannula or non-rebreather masks, ETI, intubated, SatpO2, Peripheral oxygen saturation, APACHRE, Acute Physiological and Chronic Health Evaluation, SOFA, Sepsis Organ Failure Assessment, Nx, normoxemia, Hx, hypoxemia, Hpx, hyperoxemia

      Read this article at

      ScienceOpenPublisherPMC
      Bookmark
          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          Abstract

          Patients admitted to the Intensive Care Unit (ICU) with acute hypoxemic respiratory failure automatically receive oxygen therapy to improve inspiratory oxygen fraction (FiO 2). Supplemental oxygen is the most prescribed drug for critically ill patients regardless of altitude of residence. In high altitude dwellers (i.e. in La Paz [≈3,400 m] and El Alto [≈4,150 m] in Bolivia), a peripheral oxygen saturation (SatpO 2) of 89-95% and an arterial partial pressure of oxygen (PaO 2) of 50-67 mmHg (lower as altitude rises), are considered normal values ​​for arterial blood. Consequently, it has been suggested that limiting oxygen therapy to maintain SatpO 2 around normoxia may help avoid episodes of hypoxemia, hyperoxemia, intermittent hypoxemia, and ultimately, mortality. In this study, we evaluated the impact of oxygen therapy on the mortality of critically ill COVID-19 patients who permanently live at high altitudes. A multicenter cross-sectional descriptive observational study was performed on 100 patients admitted to the ICU at the “Clinica Los Andes” (in La Paz city) and “Agramont” and “Del Norte” Hospitals (in El Alto city). Our results show that: 1) as expected, fatal cases were detected only in patients who required intubation and connection to invasive mechanical ventilation as a last resort to overcome their life-threatening desaturation; 2) among intubated patients, prolonged periods in normoxia are associated with survival, prolonged periods in hypoxemia are associated with death, and time spent in hyperoxemia shows no association with survival or mortality; 3) the oxygenation limits required to effectively support the intubated patients’ survival in the ICU are between 89% and 93%; 4) among intubated patients with similar periods of normoxemic oxygenation, those with better SOFA scores survive; and 5) a lower frequency of observable reoxygenation events is not associated with survival. In conclusion, our findings indicate that high-altitude patients entering an ICU at altitudes of 3,400 – 4,150 m should undergo oxygen therapy to maintain oxygenation levels between 89 and 93 %.

          Related collections

          Most cited references22

          • Record: found
          • Abstract: found
          • Article: not found

          Epidemiology, Patterns of Care, and Mortality for Patients With Acute Respiratory Distress Syndrome in Intensive Care Units in 50 Countries.

          Limited information exists about the epidemiology, recognition, management, and outcomes of patients with the acute respiratory distress syndrome (ARDS).
            Bookmark
            • Record: found
            • Abstract: found
            • Article: not found

            Association Between Hypoxemia and Mortality in Patients With COVID-19

            Objective To identify markers associated with in-hospital death in patients with Coronavirus Disease 2019 (COVID-19) associated pneumonia. Patients and Methods Retrospective, cohort study of 140 patients with moderate-to-critical COVID-19 associated pneumonia requiring oxygen supplementation admitted from January 28th, 2020 to February 28th, 2020, and followed up through March, 13th 2020 in Union Hospital, Wuhan, China. Oxygen saturation (SpO2) and other measures were tested as predictors of in-hospital mortality in survival analysis. Results Of 140 patients with COVID-19 associated pneumonia, 51.4% were men, with a median age of 60 years. Patients with SpO2 ≤90% were older, more likely to be men, to have hypertension and to present with dyspnea than those with SpO2 >90%. Overall, 36 (25.7%) patients died during hospitalization after a median 14-day follow-up. Higher post-oxygen supplementation SpO2 levels were associated with reduced mortality independently of age and sex (hazard ratio per 1-unit SpO2 0.93, 95% confidence interval, 0.91-0.95, P < .001). SpO2 cutoff of 90.5% yielded 84.6% sensitivity and 97.2% specificity for prediction of survival. Dyspnea was also independently associated with death in multivariable analysis (hazard ratio 2.60; 95% confidence interval 1.24-5.43, P = .01). Conclusions In this cohort of COVID-19 patients, hypoxemia was independently associated with in-hospital mortality. These results may help guide clinical management of severe COVID-19 patients, particularly in settings requiring strategic allocation of limited critical care resources.
              Bookmark
              • Record: found
              • Abstract: found
              • Article: found
              Is Open Access

              Basing Respiratory Management of COVID-19 on Physiological Principles

              The dominant respiratory feature of coronavirus disease (COVID-19) is arterial hypoxemia greatly exceeding abnormalities in pulmonary mechanics (decreased compliance) (1–3). Many patients are intubated and placed on mechanical ventilation early in their course. Projections on usage of ventilators has led to fears that insufficient machines will be available and even to proposals for using a single machine to ventilate four patients. The coronavirus crisis poses challenges for staffing, equipment, and resources, but it also imposes cognitive challenges for physicians at the bedside. It is vital that caregivers base clinical decisions on sound scientific knowledge to gain the greatest value from available resources (4). Patient oxygenation is evaluated initially using a pulse oximeter. Oxygen saturation as measured by pulse oximetry (SpO2 ) can differ from true SaO2 (measured with a CO-oximeter) by as much as ±4% (5). Interpretation of readings of SpO2 above 90% becomes especially challenging because of the sigmoid shape of the oxygen dissociation curve. Given the flatness of the upper oxygen dissociation curve, a pulse oximetry reading of 95% can signify an arterial oxygen tension (PaO2 ) anywhere between 60 and 200 mm Hg (6, 7)—values that carry extremely different connotations for management of a patient receiving a high concentration of oxygen. Difficulties in interpreting arterial oxygenation are compounded if supplemental oxygen has been instituted before a pulmonologist or intensivist first sees a patient (the usual scenario with COVID-19). Assessment of gas exchange requires knowledge of fractional inspired oxygen tension (Fi O2 ); unless the patient is breathing room air, this is not knowable in a nonintubated patient. With a nasal cannula set at 2 L/min, Fi O2 ranges anywhere between 24% and 35% (8). Arterial blood gases yield a more precise measure of gas exchange. With knowledge of PaO2 , PaCO2 , and Fi O2 , the alveolar-to-arterial oxygen gradient can be rapidly calculated. The alveolar-to-arterial oxygen gradient enables more precise evaluation of the pathophysiological basis of hypoxemia than more widely used PaO2 /Fi O2 , because this ratio may reflect changes in Po 2, Fi O2 , or both. Hypoxemia accompanied by a normal alveolar-to-arterial oxygen gradient and increase in PaCO2 signifies hypoventilation. Hypoventilation is uncommon with COVID-19. Instead, hypoxemia with COVID-19 is usually accompanied by an increased alveolar-to-arterial oxygen gradient, signifying either ventilation–perfusion mismatch or intrapulmonary shunting (9). (Diffusion problems mainly cause hypoxemia at high altitude.) If a patient’s PaO2 increases with supplemental oxygen, this signifies the presence of ventilation–perfusion mismatch. A satisfactory degree of arterial oxygenation can be sustained in these patients without recourse to intubation and mechanical ventilation. If a patient’s PaO2 does not increase with supplemental oxygen, this signifies the presence of an intrapulmonary shunt; such patients are more likely to progress to earlier invasive ventilator assistance. Circular thinking is especially dangerous when managing patients with coronavirus. After a patient starts on a therapy, it is often stated that the patient is “requiring” the said therapy. Physicians commonly state that “a patient’s oxygen requirements are going up” without making any attempt to measure oxygen consumption; it would be more accurate to simply say the patient’s level of supplemental oxygen has been increased. Reports on COVID-19 are also articulated as “patients requiring mechanical ventilation” (1–3). Only a small proportion of patients—largely those in cardiac arrest—“require” mechanical ventilation. In most instances, mechanical ventilation is instituted preemptively out of fear of an impending catastrophe. These patients are receiving mechanical ventilation, and it is impossible to prove that they “required” it when first implemented. The decision to institute invasive mechanical ventilation (involving an endotracheal tube) is based on physician judgment—clinical gestalt influenced by oxygen saturation, dyspnea, respiratory rate, chest radiograph, and other factors (10). Many patients with COVID-19 are intubated because of hypoxemia; yet, they exhibit little dyspnea or distress. Humans do not typically experience dyspnea until PaO2 falls to 60 mm Hg (or much lower) (11). I was once a volunteer in an experiment probing the effect of hypoxemia on breathing pattern (12); my pulse oximeter displayed a saturation of 80% for over 1 hour, and I was not able to sense differences between saturations of 80% and 90% (and above). When assessing dyspnea, it is imperative to ask open-ended questions. Leading questions, with the goal of seeking endorsement, can be treacherous (4). Tachypnea in isolation should rarely constitute the primary reason to intubate; yet, it commonly does (10). Tachypnea is the expected response to lung inflammation that produces stimulation of irritant, stretch, and J receptors (11). Respiratory rates of 25–35 breaths per minute should not be viewed as ipso facto (knee jerk) justification for intubation, but rather the expected physiological response to lung inflammation. It is incorrect to regard tachypnea as a sign of increased work of breathing; instead, work is determined by magnitude of pleural pressure swings and tidal volume (9). Palpation of the sternomastoid muscle, and detection of phasic (not tonic) contraction, is the most direct sign on physical examination of increased work of breathing (4). Pulmonary infiltrates are commonly seen with COVID-19. Infiltrates on their own are not an indication for mechanical ventilation. Across four decades, I have been seeing patients with extensive pulmonary infiltrates managed with supplemental oxygen. It is only when pulmonary infiltrates are accompanied by severely abnormal gas exchange or increased work of breathing that intubation becomes necessary. There is a fear that without mechanical ventilation, COVID-19 will produce organ impairment. Evidence of end-organ damage is difficult to demonstrate in patients with PaO2 above 40 mm Hg (equivalent to oxygen saturation of ∼75%) (10). The amount of oxygen delivered to the tissues is the product of arterial oxygen content and cardiac output. In patients with decreased oxygen delivery, oxygen extraction initially increases and oxygen consumption remains normal (13). When oxygen delivery decreases below a critical threshold, this extraction mechanism is no longer sufficient, and total body oxygen consumption decreases proportionally; metabolism changes from aerobic to anaerobic pathways, and vital organ function becomes impaired. This critical threshold does not arise in critically ill patients until oxygen delivery decreases to <25% of the normal value (14). Once a patient is placed on a ventilator, the key challenge is to avoid complications (15). Mechanical ventilation (in and of itself) does not produce lung healing; it merely keeps patients alive until their own biological mechanisms are able to outwit the coronavirus. The best way to minimize ventilator-associated complications is to avoid intubation unless it is absolutely necessary (16, 17). The surest way to increase COVID-19 mortality is liberal use of intubation and mechanical ventilation. Within 24 hours of instituting mechanical ventilation, physicians need to consciously evaluate patients for weanability (16, 17). This step is especially important during the COVID-19 pandemic to free up a ventilator for the next patient. Deliberate use of physiological measurements—weaning predictors, such as frequency/Vt ratio (18)—alerts a physician that a patient is likely to succeed in weaning before the physician would otherwise think. These tests achieve their greatest impact if performed when a physician believes that the patient is not yet ready for weaning. Once a patient is ready for a trial of weaning, the most efficient method is to employ a T-tube circuit (19); flow-by (with positive end-expiratory pressure at zero and pressure support at zero) is equally efficient while avoiding environmental contamination. Patients with COVID-19 exhibit severe respiratory failure and differ from the easy-to-wean patients in recent randomized controlled trials. Never before in 45 years of active practice have I witnessed physicians coping with inadequate medical resources—specifically a shortage of ventilators. Given this situation, it is pivotal that caregivers have the requisite knowledge to interpret arterial oxygenation scientifically, know when to institute mechanical ventilation, and equally know how to remove the ventilator expeditiously to make it available for the next patient.
                Bookmark

                Author and article information

                Journal
                Respir Physiol Neurobiol
                Respir Physiol Neurobiol
                Respiratory Physiology & Neurobiology
                Published by Elsevier B.V.
                1569-9048
                1878-1519
                10 February 2022
                May 2022
                10 February 2022
                : 299
                : 103868
                Affiliations
                [a ]Clínica Los Andes del Grupo Embriovid, La Paz, Bolivia
                [b ]Hospital Agramont, El Alto, Bolivia
                [c ]Hospital del Norte, El Alto, Bolivia
                [d ]High Altitude Intensive Care Medicine International Group, GIMIA, Bolivia
                [e ]High Altitude Intensive Care Medicine International Group, GIMIA, Peru
                [f ]High Altitude Intensive Care Medicine International Group, GIMIA, Colombia
                [g ]High Altitude Pulmonary and Pathology Institute (HAPPI-IPPA), La Paz, Bolivia
                [h ]Centre de Recherche de l’Institute Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, Québec, Canada
                Author notes
                [* ]Corresponding author at: Faculté de Médecine, Université Laval, Centre de Recherche, IUCPQ, M2-13, 2725 chemin Ste-Foy Québec, Québec, G1V 4G5, Canada.
                Article
                S1569-9048(22)00027-1 103868
                10.1016/j.resp.2022.103868
                8828373
                35150939
                425df21e-ea99-4de8-9376-af24b1025ef6
                © 2022 Published by Elsevier B.V.

                Since January 2020 Elsevier has created a COVID-19 resource centre with free information in English and Mandarin on the novel coronavirus COVID-19. The COVID-19 resource centre is hosted on Elsevier Connect, the company's public news and information website. Elsevier hereby grants permission to make all its COVID-19-related research that is available on the COVID-19 resource centre - including this research content - immediately available in PubMed Central and other publicly funded repositories, such as the WHO COVID database with rights for unrestricted research re-use and analyses in any form or by any means with acknowledgement of the original source. These permissions are granted for free by Elsevier for as long as the COVID-19 resource centre remains active.

                History
                : 29 October 2021
                : 6 January 2022
                : 8 February 2022
                Categories
                Article

                Anatomy & Physiology
                covid-19,liberal oxygen therapy,intensive care unit,high-altitude,central respiration,normoxemia,hypoxemia,hyperoxemia,icu, intensive care unit,fio2, inspired oxygen fraction,pao2, arterial partial pressure of oxygen,pb, barometric pressure,ards, acute respiratory distress syndrome,niv, non-invasive ventilation,hfnc/nrm, high-flow nasal cannula or non-rebreather masks,eti, intubated,satpo2, peripheral oxygen saturation,apachre, acute physiological and chronic health evaluation,sofa, sepsis organ failure assessment,nx, normoxemia,hx, hypoxemia,hpx, hyperoxemia

                Comments

                Comment on this article